1. Field of the Invention
The present invention relates to a SAL (Soft Adjacent Layer) bias system magnetoresistive head used for magnetic data storage devices such as hard disks, and to a magnetic read/write device employing it.
2. Description of the Related Art
The recent increase in capacities of magnetic read/write devices used as external storage devices for computers has brought a demand for higher recording densities. As a means of meeting this demand, progressive development has been pursued on high density MR heads as magnetic heads. However, the magnetoresistive films (hereunder abbreviated to MR films) used in MR heads produce nonlinear outputs with respect to the external magnetic field when no biasing magnetic field is present. Consequently, in order to obtain a reproduced waveform corresponding to the magnetic field generated by the magnetic memory medium, it is necessary to apply a biasing magnetic field to the MR film by some method to cause the MR film to operate in a linear region. As one method of achieving this there has been proposed the SAL bias system, which gives a high biasing effect at low current.
Materials used for biasing soft magnetic films are preferred to have high electrical resistance, low magnetic resistance and a low magnetostriction constant, and are generally NiFeX (X.dbd.Cr, Rh, Nb) based alloys. Also, the direction of the easy axis of magnetization for the biasing soft magnetic film is usually oriented parallel to the direction of the easy axis of magnetization for the MR film. In some cases, as in Japanese Unexamined Patent Publication No. 6-338034, the direction of the easy axis of magnetization for the biasing soft magnetic film and the direction of the easy axis of magnetization for the MR film are oriented roughly perpendicular to each other, to thus inhibit the magnetoresistive effect produced on the biasing magnetic film and allow reading of the magnetic recording device even at a low sense current.
In this conventional construction the biasing soft magnetic film is still an NiFeX (X.dbd.Cr, Rh, Nb) based alloy and thus the value of the electrical resistance is not very high. Furthermore, the value of the saturation flux density is also insufficient and therefore the film thickness must be increased to an adequate degree to allow its use as a biasing soft magnetic film. Thus, when a sense current flows through the head there is more current flowing to the biasing soft magnetic film and less of the current flowing to the MR film, creating a problem wherein the head output can only be raised by increasing the value of the sense current. Also, when the direction of the easy axis of magnetization for the biasing soft magnetic film is oriented perpendicular to the direction of the easy axis of magnetization for the MR film, if a NiFe-based alloy is used for the biasing magnetic film the direction of the easy axis of magnetization is altered by heat treatment because of induced anisotropy of the NiFe-based alloy, thus resulting in the problem of unstable reproduction by the head.
In addition, Japanese Unexamined Patent Publication No. 5-182148 proposes, as the biasing soft magnetic film, a soft magnetic film composed of a laminate of 2 or more different magnetic materials, for example a soft magnetic film composed of a laminate of a NiFeX-based alloy film and an FeN film. This publication teaches that the FeN film alone is unsuitable for a biasing soft magnetic film, but that in combination with the NiFeX-based alloy film it is possible to have suitable soft magnetic characteristics and saturation magnetization. However, since this laminated film uses a NiFeX-based alloy film as the principal biasing soft magnetic film which is modified with the FeN film, it fails to solve the aforementioned problems associated with NiFeX-based alloy films.
The present invention overcomes these problems of the prior art, and its object is to provide an MR head with high reproduction output, which is capable of the accurate reproduction of magnetic recording media.